This program project is a multi-disciplinary and collaborative approach to the investigation of several fundamental mechanisms involved in the immune response and lymphocyte biology. This program focuses on the biochemistry, genetics and functions of the products of the major histocompatibility complex (MHC), the nature of receptors on immunocompetent cells. Individual projects represent collaborative efforts among 2 or more investigators and/or laboratories to investigate: 1) Immunologic properties of liposomes containing MHC antigens; 2) HLA-D region structure and function in the regulation of responses of human lymphocytes; 3) Chemistry and structure of T cell and macrophage Ia antigens; 4) Immunochemistry and function of antigen-specific suppressor T cell factors; 5) Antigen-specific T cell factors that modulate myeloma cell differentiation; 6) Ia antigen expression on clonally propogated murine macrophages; 7) Immunogenetics and functions of the murine complement system; 8) Lactoperoxidase as a specific immunological probe; 9) Altered T cell reactivity induced by specific immune manipulation including tolerance induction and thymus gland grafting of nude mice; 10) Murine antibodies of limited heterogeneity specific for heterologous insulin and proinsulin; and 11) The role of IgG3 in the immune deficiency of CBA/N mice. These projects are supported by Core Animal Production, Reagent Production and Hybrid Cell Facilities.